Method for reducing oxysulfur compounds

ABSTRACT

Inorganic, water-soluble oxysulfur compounds are reduced by contacting an aqueous solution of the oxysulfur compound and hydrogen with a bimetallic catalyst at reduction conditions. The bimetallic catalyst comprises catalytically effective amounts of a metallic sulfide selected from sulfides of the transition metals from group VI and of a metallic sulfide selected from the sulfides of the transition metals of group VIII combined with a porous carrier material. A specific example of the disclosed invention is a method for reducing an inorganic, water-soluble thiosulfate compound to a sulfide compound by contacting an aqueous solution of the thiosulfate compound and hydrogen, at reduction conditions, with a catalyst comprising a combination of catalytically effective amounts of molybdenum sulfide and of cobalt sulfide with a porous carrier material.

[ 1 June5,1973

[54] METHOD FOR REDUCING OXYSULFUR COMPOUNDS [75] Inventor: Peter Urban,Northbrook, Ill.

[73] Assignee: Universal Oil Products Company,

Des Plaines, 111.

22 Filed: Feb.8, 1971 21 Appl.No.:l13,722

[56] References Cited UNITED STATES PATENTS 11/1912 80110 et a1...23/137 7/1927 Naef ....23/137 1,916,803 7/1933 Ley et a1... ....23/l372,093,504 9/1937 Zirngibl.... ....23/137 3,558,272 1/1971 Urban....23/137 Primary Examiner-Edward Stern Attorney-James R. Hoatson, Jr.and Thomas K. Mc- Bride [57] ABSTRACT Inorganic, water-soluble oxysulfurcompounds are reduced by contacting an aqueous solution of the oxysulfurcompound and hydrogen with a bimetallic catalyst at reductionconditions. The bimetallic catalyst comprises catalytically effectiveamounts of a metallic sulfide selected from sulfides of the transitionmetals from group VI and .of a metallic sulfide selected from thesulfides of the transition metals of group VIII combined with a porouscarrier material. A specific example of the disclosed invention is amethod for reducing an inorganic, water-soluble thiosulfate compound toa sulfide compound by contacting an aqueous solution of the thiosulfatecompound and hydrogen, at reduction conditions, with a catalystcomprising a combination of catalytically effective amounts ofmolybdenum sulfide and of cobalt sulfide with a porous carrier material.

23 Claims, N0 Drawings METHOD FOR REDUCING OXYSULFUR COMPOUNDS Thesubject of the present invention is a method for the catalyticconversion of an inorganic, water soluble oxysulfur compound to asulfur-containing compound which has its sulfur component in a lowervalance state than the oxysulfur compound primarily the conversion ofthe oxysulfur compound to the corresponding sulfide .compound. Morespecifically, the present invention relates to a novel catalytic methodwhich utilizes controlled amounts of hydrogen in conjunction with aspecial bimetallic catalyst to effect selective reduction of theoxidation state of the sulfur component of the oxysulfur compound. Thebimetallic catalyst utilized in this method essentially comprisescatalytically effective amounts of a metallic sulfide component,selected from the sulfides of the transition metals of group VI, and ofa metallic sulfide component, selected from the sulfides of thetransition metals of group VIII, combined with a porous carriermaterial. In one aspect the present invention involves a method for theselective, catalytic reduction of a water-soluble, inorganic sulfitecompound to the corresponding sulfide compound. In another importantaspect the present invention is a selective, catalytic method forselectively reducing a water-soluble thiosulfate compound to. thecorresponding sulfide compound. In a more limited aspect, the presentinvention relates to a method for reducing a water-soluble thiosulfatecompound to the corresponding sulfide compound using hydrogen as thereducing agent and a catalyst comprising catalytically effective amountsof cobalt sulfide and molybdenum sulfide combined with a suitable porouscarrier material.

As part of the price that has to be paid for a modern industrialsociety, aqueous solutions of oxysulfur compounds are produced as majorproducts or by-products of a number of significant industrialactivities. By use of the term 105 oxysulfur compounds, it is intendedto cover all common water-soluble compounds of sulfur and oxygen whichare typically found in industrial waste or process streams, such assulfuric acid, sulfurous acid and water-soluble salts thereof,thiosulfuric acid and water-soluble salts thereof and the polythionicacids ((H S O wherein n may have any value from 2 to 6 inclusive) andwater soluble salts thereof. These aqueous solutions of oxysulfurcompounds are quite prevelant in modern industry primarily because ofthe widespread utilization of sulfur as a basic reactant or ingredientin many chemical processes and because of the presence of substantialquantities of sulfur in various forms in the fuel used to generate themajor portion of energy consumed in a modern industrial economy. Theelectrical utility industry is, for example, currently faced with amajor pollution problem caused by the widespread practice of burningcoal and fuel oil containing significant amounts of sulfur in its powerstations. During the course of the combustion of the sulfur-containingfuel, the sulfur is converted to oxides of sulfur, primarily sulfurdioxide, with attendant production of a flue or stack gas streamcontaining substantial amounts of sulfur oxides. Removal of these sulfuroxides from this flue gas, by means of conventional scrubbing processeswith aqueous absorbents, quite commonly results in an aqueous streamcontaining signifcant amounts of water-soluble oxysulfur compounds,primarily they are water-soluble sulfite compounds.

Likewise aqueous stream containing oxysulfur compounds can be producedby wet scrubbing SO containing waste gas streams produced in otherindustrial activities such as the smelting of sulfur-bearing ores, therefining of sulfur-containing crude oils, the synthesis of sulfuricacid, the sulfonation of hydrocarbons, the production of coke, theproduction of sulfur in a Claus unit, the production of paper via awoodpulping process and the like industrial processes.

Aqueous solutions containing water-soluble, inorganic thiosulfatecompounds are commonly available as undesired side or drag streams frommany economically significant industrial processes in the chemical,petroleum and steel industries. For instance, in the petroleum industry,an aqueous solution containing ammonium thiosulfate is commonly producedas a drag stream from sulfur recovery systems that employ an oxidationtechnique. These sulfur recover systems are usually designed to enablethe recovery of elemental sulfur from ammonium hydrosulfide solutionswhich are byproducts of such typical refinery processes ashydrorefining, hydrocracking, catalytic cracking and the like. See forexample the sulfur recovery systems disclosed in US. Pat. Nos.3,536,619; 3,536,618; 3,531,395 and 3,530,063.

Another common source for thiosulfatecontaining aqueous solutions isfound in connection with scrubbing processes designed to sweeten naturalgas to purify coal gas or town gas and the like processes to cleanuprefinery gas streams where hydrogen sulfide is scrubbed from a gaseousmixture with an aqueous absorbent to produce a rich absorbent streamwhich is thereafter regenerated with oxygen. For example in the Seaboardprocess, where the absorbent is an aqueous solution of sodium carbonateand the regeneration step essentially involves stripping the absorbedhydrogen sulfide from the rich absorbent solution with large quantitiesof air, the air used in this regeneration step tends to oxidize some ofthe absorbed hydrogen sulfide to sodium thiosulfate which causes abuild-up of thiosulfate in the absorbent solution. This thiosulfatebyproduct production problem is commonly handled by periodically orcontinuously withdrawing a drag stream from the process containingsodium thiosulfate and adding a fresh alkaline reagent. Similar problemsof thiosulfate by-product formation are also found in other H 8scrubbing processes that employ oxygen to regenerate the rich absorbentregeneration step such as in the Ferrox Process, the Thylox Process, thePerox Process and the Nickel Process. In all of these wet H 5 scrubbingprocesses an inevitable side reaction appears to be one leading to theformation of water-soluble thiosulfate salt by-products, which thenaccumulate in the scrubbing solution until these pressures becomedetrimental. The net amount of the thiosulfate byproduct being producedmust, therefore, be continuously or periodically purged from thescrubbing system by discarding a drag stream containing a water-solublethiosulfate compound.

Regardless of the source of the aqueous stream containing oxysulfurcompounds, it is clear that there is a substantial need for an effectiveand simple method for treating these types of solutions in order toremove the oxysulfur compound therefrom and allow either reuse of theresulting treated aqueous solution in the process which produced it orto enable the discharge of the water stream into sewers, rivers orstreams without causing any substantial pollution problem. The firstalternative is particularly attractive when the sulfoxidecontainingsolution also contains other valuable reagents such as the Thyloxprocess wherein the drag stream which is withdrawn from the process inorder to purge the undesired thiosulfate by-product, also containssodium carbonate and arsenic trioxide. In addition, the glowingsensitivity of the public to the numerous adverse effect ofindiscriminate discharge of gaseous and aqueous waste streams containingoxysulfur compounds provides an additional incentive for treating theseoxysulfur compound-containing aqueous solutions in order to remove thedetrimental sulfurcontaining compounds prior to the discharge of thesolutions into conventional sewage facilities.

In one specific case of particular interest, hydrorefining orhydrocracking of petroleum distillates containing nitrogenous andsulfurous contaminants, large quantities of ammonium and hydrogensulfide are present in the effluent stream from the reaction zone, andthese contaminants are generally absorbed in an aqueous solution whichis injected into the effluent train of cooling means and separatingzones associated with the hydrocarbon conversion process. This resultsin an aqueous waste stream containing ammonium hydrosulfide (NH,,HS)which can thereafter be subjected to a catalytic oxidation step in orderto recover sulfur therefrom or to reduce the biological oxygen demandthereof. Despite stringent precautions, a minor amount of thiosulfatesalt (i.e. (NH S is inevitably formed as a side product in thiscatalytic oxidation step. The resulting ammonium thiosulfate-containingaqueous solution withdrawn as effluent from this oxidation step cannotordinarily be reused to recover an additional portion of ammoniumhydrosulfide because, if it is injected into the effluent trainassociated with the hydrorefining of hydrocracking process, the hydrogensulfide and/or ammonium hydrosulfide present in the effluent from thereaction zone can react with the ammonium thiosulfate to produce freesulfur which can contaminate the hydrocarbon product from thishydrocarbon conversion process leading to severe corrosion problems indown-stream equipment. There is thus a substantial need for a method ofefficiently and conveniently treating an aqueous solution containingammonium thiosulfate in order to allow reuse of the aqueous streamwithin the hydrocarbon conversion process to absorb additionalquantities of hydrogen sulfide.

Another specific case of particular interest involves the wet-scrubbingof sulfur dioxide from SO containing gas streams, which are produced bythe combustion of sulfur-containing fuels, the smelting ofsulfur-containing ores and the like industrial activities (as explainedhereinbefore) to produce a rich aqueous absorbent stream containingsalts of sulfurous acid. A common procedure involves the use of anabsorbent which essentially is a solution of a relatively inexpensivealkaline reagent such as the hydroxide and carbonate compounds ofammonia, the alkali metals and the alkaline earth metals. After thissolution is used to absorb $0 from flue gas, a rich absorbent streamcontaining the corresponding sulfite compound for example, ammoniumsulfite and/or bisulfite and the like compoundsis obtained. l haverecently discovered a novel procedure for treating this type ofsulfitecontaining aqueous solution which minimizes the amount ofundesired, intractable sulfate compounds formed during the regenerationstep on this absorbent solution. This treatment procedure essentiallyinvolves the production of an aqueous stream containing a water-soluble,inorganic thiosulfate compound as an intermediate in the regenerationoperation. Both the sulfitecontaining aqueous stream withdrawn from theS0 scrubber and the thiosulfate-containing stream produced in accordancewith my recently developed procedure are aqueous solutions containingoxysulfur compounds which require additional treatment in order toregenerate the scrubbing solution so that it can be recycled to the SO-scrubbing step. Thus, in this specific embodiment, there is also a needfor a treatment procedure which can efficiently and conveniently operateon these types of oxysulfur-containing solutions in order to regeneratethe aqueous scrubbing solution.

The problem addressed by the present invention is, therefore, to providea method for efficiently, economically and conveniently treating anoxysulfur-containing solution in order to convert the oxysulfur compoundcontained therein to a species which can easily be removed from theresulting treated solution.

I have now found a procedure for converting these water-solubleoxysulfur compounds into the corresponding sulfide compound in a highlyselective manner. The resulting sulfide compound can then be easilyremoved from the resulting treated solution by a conventional procedurefor liberating a sulfide compound from an aqueous solution such as byadding a relatively strong acid (i. e. stronger than H 8) in an amountsufficient to lower the pH to the point where hydrogen sulfide isliberated or by a conventional H S-Stripping step. In some cases, thesulfide-containing treated aqueous stream produced by the method of thepresent invention may be useful per se or may be directly charged to aprocess for converting aqueous solutions of sulfide to elemental sulfursuch as the process described in my US. Pat. No. 3,034,865.

The basic concept of the method of the present invention emanated frommy efforts to develop a more active and selective catalyst for thereduction of aqueous solutions of oxysulfur compounds with hydrogen.During the course of these investigations I discerned that a synergisticeffect could be obtained in this reaction if a special bimetalliccatalyst was utilized. My finding here was essentially that a bimetalliccatalyst, comprising catalytically effective amounts of a first metallicsulfide component selected from the transition metals from group VI ofthe Periodic Table and a second metallic sulfide component selected fromthe sulfides of the transition metals of group VIII of the PeriodicTable combined with a porous carrier material, accelerates thisreduction reaction in a manner sharply superior to that observed whenthe catalyst utilized only contains one of these metallic sulfidecomponents. In other words, I have determined that a catalyst containingboth of these metallic sulfide components is materially more active andselective than a catalyst containing only one of them in promoting theselective reduction of oxysulfur compounds to the corresponding sulfidecompounds in an aqueous solution when hydrogen is used as the reducingagent. For example I have ascertained that a catalyst, comprisingcatalytically effective amounts of molybdenum sulfide and cobalt sulfidecombined with an activated carbon carrier material, is sharply superiorto a catalyst containing only one of these sulfides in accelerating areaction between an produce sodium hydrosulfide.

It is, accordingly, an object of the present invention to provide animproved method for catalytically reducing an inorganic water-solubleoxysulfur compound with hydrogen to a sulfide compound. Another objectis to provide a very active bimetallic catalyst which is uniquelycapable of accelerating the reaction between an aqueous solution ofoxysulfur compounds and hydrogen to selectively produce sulfide. Yetanother object is to provide a bimetallic catalyst for this oxysulfurcompound reduction reaction which enables the selective production ofsulfide at relatively mild conditions of temperature and pressure.

In brief summary, a broad embodiment of my invention involves a methodfor reducing an inorganic, water-soluble oxysulfur compound to a sulfidecompound. This method essentially comprises contacting an aqueoussolution of the oxysulfur compound and hydrogen with a bimetalliccatalyst at reduction conditions. The bimetallic catalyst utilizedcomprises a combination of catalytically effective amounts of a groupVIB metallic sulfide component, and of a group VIII metallic sulfidecomponent with a porous carrier material.

Another embodiment of the present invention involves a process asoutlined above wherein said oxysulfur compound is a water-soluble,inorganic sulfite compound.

Another embodiment involves the method first outlined above wherein theoxysulfur compound is a water-soluble, inorganic thiosulfate compound.

In a more limited embodiment, the present invention is a method forreducing an inorganic, water-soluble thiosulfate compound to a sulfidecompound. The method essentially involves contacting an aqueous solutionof the thiosulfate compound and hydrogen with a catalyst, comprising acombination of catalytically effective amounts of molybdenum sulfide andof cobalt sulfide with a porous carriermaterial, at reductionconditions. Moreover, hydrogen is preferably utilized in an amountselected to correspond to a mole ratio of hydrogen to thiosulfatecompound contained in the solution of about 40: l and the reductionconditions preferably include a temperature of about 50 to about 350 C.and a pressure at least sufficient to maintain a portion of the aqueoussolution in the liquid phase.

In another limited embodiment, the present invention is a method asoutlined above in the last embodiment where the catalyst utilizedcomprises a combination of a cobalt sulfide component and of amolybdenum sulfide component with a carbonaceous carrier material inamounts selected to result in a composite containing, on an elementalbasis, about 0.01 to about wt. percent molybdenum and about 0.1 to aboutwt. percent cobalt.

Other objects and embodiments of the present invention include specificdetails about particular oxysulfur compounds that can be reducedthereby, preferred amounts and sources for the hydrogen reducing agent,particularly preferred reduction conditions for use therein, preferredcatalysts for use therein and particularly beneficial flow schemes foruse therewith. All of these facets of the present invention arehereinafter disclosed in the following detailed description of theessential and preferred features of the instant method.

One reactant for the method of the present invention is a water-solubleoxysulfur compound. As previously explained the use of the termoxysulfur compound" is intended to cover the common inorganic,water-soluble compound of oxygen and sulfur that are prevelant in modernday industry. It is intended to include within the scope of this termall compounds of oxygen and sulfur that are soluble in water and arecapable of being reduced by hydrogen in the presence of a metallicsulfide-containing catalyst. One kind of oxysulfur compound that isincluded within this definition are the water-soluble inorganic sulfitecompounds. These include sulfurous acid, ammonium sulfite and bisulfite,the alkali metal sulfites and bisulfites, the alkaline earth metalsulfites and bisulfites and the like sulfites. Another class ofoxysulfur compounds suitable for use herein are the inorganic,water-soluble thiosulfate com pounds such as ammonium thiosulfate, thealkali metal thiosulfate, the alkaline earth metal thiosulfate and thelike thiosulfates. Typically, excellent results are obtained when theoxysulfur compound is ammonium thiosulfate or sodium thiosulfate. Yetanother class of oxysulfur compounds which can be treated by the methodof the present invention are the inorganic polythionic compounds such asthe polythionic acids (i. e. H S O where It may have a value from 2 to 6inclusive) the ammoniumpolythionates, the alkali metal polythionates,the alkaline earth metal polythionates and the like salts of thepolythionic acids. Still another large class of compounds of sulfur andoxygen that are included within the scope of the oxysulfur compounds arethe water-soluble, inorganic sulfate compounds. These last compoundsare, in general, very difficult to treat by the method of the presentinvention unless the pH of the solution containing them is adjusted to avery low level such that free sulfuric acid would be present in thesolution. That is, the only sulfate compound that is readily amenable totreatment by the present invention is sulfuric acid. Ordinarily, bestresults are obtained when the oxysulfur compound is either a sulfitecompound or a thiosulfate compound.

As indicated above, it is an essential feature of the instant methodthat the oxysulfur compound is charged thereto in an aqueous solution.The amount of oxysulfur compound contained in this solution can rangefrom relatively small amounts up to the solubility limit of theparticular oxysulfur compound in water at the conditions utilized in thepresent method. Typically, the amount of oxysulfur compound contained inthe input aqueous solution will be sufficient to constitute about 0.1 toabout 30 wt. percent of the solution. For example, excellent resultshave been obtained with the present method when an aqueous solutioncontaining about 20 wt. percent of sodium thiosulfate is chargedthereto.

The other essential reactant for the present invention is hydrogen. Thehydrogen stream for use herein may be obtained from any suitable sourceor may be prepared in any suitable manner. In addition, it may comprisesubstantially pure hydrogen or a mixture of hydrogen with otherrelatively inert gases, such as a mixture of hydrogen and nitrogen, amixture of hydrogen and steam, a mixture of hydrogen with carbon dioxideor carbon monoxide and the like gaseous streams. One acceptable type ofhydrogen stream for use herein is obtained by a controlled partialcombustion ofa hydrocarbon stream, such as a naphtha stream, a naturalgas stream, a heavy fuel oil stream and the like hydrocarbon streams, ina non-catalytic reaction with air or pure oxygen at relatively hightemperatures of 1,000 to 3,000 or more F. and a pressure of about 1 toabout 20 atmospheres or more. Another acceptable source for a hydrogenstream is the excess recycle gas obtained from the various hydrocarbonconversion processes which have a net hydrogen make such as a reformingprocess, a dehydrogenation process and the like. Yet another commonsource for an acceptable hydrogen stream is a catalytic steam reformingreaction between a hydrocarbon stream, selected from the light naphthas,natural gas streams, propane streams, LPG streams and the like, andsteam. This reaction typically involves use of a nickel-containingcatalyst at temperatures of 1,000 to 2,000 F. and a pressure of to 50atmospheres coupled with a suitable CO to CO shift reaction step. Ofcourse, a relatively pure hydrogen stream can be easily prepared by anelectrolysis procedure if desired. Least preferred of the availablecommercial sources of hydrogen stream is a stream produced bygasification of a solid carbonaceous material with oxygen or steam;however, such a stream can be utilized if absolutely necessary.

The amount of hydrogen charged to the current method is preferablysufficient to provide at least the stoichiometric amount of hydrogennecessary to reduce all of the sulfur component of the oxysulfurcompound to the sulfide state. For example, when the oxysulfur compoundis a thiosulfate compound, this stoichiometric amount is 4 moles of Hper mole of thiosulfate. Likewise, when the oxysulfur compound is asulfite compound the stoichiometric amount necessary to reduce sulfiteto sulfide is three moles of hydrogen per mole of sulfite compound. Inall cases, it is preferred to operate with an amount of hydrogen whichis substantially in excess of this minimum value-especially about 1.5 toabout times this minimum value. For example, when the oxysulfur compoundis a thiosulfate compound, it is preferred to use about 6 to about 40moles of hydrogen per mole of thiosulfate. It is, of course, understoodthat in the preferred case where excess hydrogen is utilized, unreactedhydrogen present in the effluent from the reduction step can be easilyseparated therefrom in a suitable gas-liquid separating zone andrecycled through suitable compressive means to supply at least a portionof the necessary hydrogen for the reduction reaction.

An essential feature of the present invention involves the use of acatalyst comprising a combination of catalytically effective amounts ofagroup VIB metallic sulfide component and of a group VIII metallicsulfide component with a porous carrier material. Considering first theporous carrier material, it is preferred that the material be a porousadsorptive high surface area support having a surface area of about 100to about 1,000 or more m"/g. The porous carrier material should berelatively refractory to the conditions utilized in the reduction zoneand it is intended to include within the scope of the present invention,carrier materials which have traditionally been utilized to supporttransition metals in catalysis such as: (l) activated carbon, coke, orcharcoal; (2) silica or silica gel, silicon carbide, clays, andsilicates including those synthetically prepared and naturallyoccurring, which may or may not be acid treated for example, attapulgusclay, china clay, diatomaceous earth, fullers earth, kaolin, kieselguhr,etc.; (3) ceramics, porcelain, crushed firebrick, bauxite; (4)refractory inorganic oxides such as alumina, tintanium dioxide,zirconium dioxide, chromium oxide, zinc oxide, magnesia, thoria, boria,silicaalumina, silica-magnesia, alumina-boria, silicazirconia, etc.; (5)crystalline aluminosilicate such as naturally occurring or syntheticallyprepared mordenite and/or faujasite, either in the hydrogen form or in aform which has been treated with multivalent cations; and, 6)combination of one or more elements from these groups.

One preferred class of porous carrier materials for use in the presentinvention are relatively carbonaceous materials such as activatedcarbons, the various types of charcoal, coke and refractory inorganicoxides having carbonaceous material deposited thereon. An example ofthis last type of carrier material is a refractory inorganic oxide whichhas seen service in a hydrocarbon conversion reaction until it has 5 to30 percent or more wt. percent carbon deposited thereon. Within thisclass of preferred carbonaceous carrier materials, best results areordinarily obtained when the carrier material is an activated carbon.These activated carbon carrier materials are commercially availableunder the trade names of Norit, Nuchar, Darco, and the like. Of course,any similar activated carbon material known to those skilled in the artcan'also be utilized in the present catalyst. Especially preferredactivated carbon carrier materials have an apparent bulk density ofabout 0.1 to about 1 g/cc and surface area characteristics such that theaverage pore diameter is about 10 to 1,000 Angstroms, the pore volume isabout 0.1 to about 1 cc/g and the surface area is about to about 1,000or more m /g. In general, excellent results are typically obtained withan activated carbon carrier material (e. g. a Darco activated carbon)with a relatively small particle size (e. g. about 10 to about 30 meshU.S. standard sieve size) having an apparent bulk density of about 0.43g/cc, a pore volume of about 0.5 1 8 g/cc and a surface area of about800 to about 1,100 m /g. In addition, the most preferred activatedcarbon carrier materials for use in the present catalyst are the onesthat are classified as having a strong affinity for water; that is, theones that are lyophilic.

Another preferred class of porous carrier materials are the refractoryinorganic oxides, with alumina being most preferred among these.Suitable alumina carrier materials are the transition aluminas known asgamma- ,eta-, and thetaalumina. A gamma-alumina carrier materialordinarily is the best of these. In general, excellent results areobtained with a gamma-alumina carrier material which is used in the formof relatively small particles (typically about one-sixteenth inch indiameter) having an apparent bulk density of about 0.5 g/cc, a porevolume of about 0.5 cc/g and a surface area of about m /g.

The first metallic sulfide component of the catalyst used in the methodof the present invention is selected from the group VIB metallic sulfidecompounds; that is the sulfides of the group Vl transition metals of thePeriodic Table. Included within the scope of this characterization arethe sulfide compounds of chromium, molybdenum, tungsten and mixturesthereof. The preferred group VIB component is molybdenum sulfide.Although this component may initially exist within the catalyst in aform other than the sulfide form such as the oxide, halide, oxyhalide,elemental metal and the like, it very rapidly becomes sulfided duringuse in the present reduction reaction and is, consequently, re-

ferred to herein as being in the sulfide state. As indicated hereafter,it is preferred to prepare the catalyst so that the group VIB metalliccomponent is initially present as the metallic sulfide. This componentcan be utilized in any amount which is catalytically effective, with theamount typically being selected so that the final catalyst containsabout 0.01 to about 10 wt. percent of this component, calculated on anelemental metal basis. A particularly preferred catalyst, for example,would contain, on an elemental basis, about 0.5 to about wt. percentmolybdenum.

This group VI transition metal component may be incorporated in thefinal composition in any suitable manner and at any stage in thepreparation thereof. One method involves impregnation of the porouscarrier material with a suitable solution of the group VI transitionmetal. Another method is the ion-exchange method in which a solution ofa suitable compound of the group VI transition metal, wherein the metalis present as an exchangeable ion, is contacted with the carriermaterial. Still another method involves cogellation or coprecipitationof the group VIB component with the carrier material when it is arefractory inorganic oxide. The preferred method involves impregnationof the carrier material with a solution containing the group VItransition metal; for example, excellent results are obtained byimpregnating with an aqueous solution of suitable group VIB salts suchas ammonium tungstate, sodium tungstate, molybdenum tetrabromide,molybdic acid, chromium dibromide, chromium dichloride, chromiumnitrate, sodium chromate, ammonium molybdate, etc. typically followed byconventional drying and calcination steps. This component may be addedbefore during or after the addition of the group VIII metallic sulfidecomponent, with best results typically obtained with sequentialimpregnation steps which are separated by a sulfiding treatment. Forexample, in the case of the preferred molybdenum sulfideand cobaltsulfide-containing catalyst, excellent results are obtained byimpregnating the carrier material first with cobalt acetate, then dryingand treating the resulting cobalt-impregnation material with H S untilan equilibrium condition is established, thereafter, in a secondimpregnation step, adding the molybdenum component by means of animpregnation solution containing molybdic acid and finally drying andtreating once again with sulfide.

The second metallic sulfide component of the catalyst of interest hereis selected from the group VIII sulfide compounds; that is the sulfidecompounds of the group VIII transition metals of the Periodic Table.Included within the scope of this classification are the sulfidecompounds of the iron group metals (i. e. iron, cobalt, and nickel) andthe platinum group metals (i.e. platinum, iridium, osmium, palladium,rhodium and ruthenium Best results are ordinarily obtained when thissecond metallic sulfide component is an iron group metallic sulfide, andthe most preferred iron group metallic sulfide is cobalt sulfide. As wasthe case with the first metallic sulfide component, this component mayinitially exist with the catalyst as a nonsulfide compound or as theelemental metal, with transition to the sulfide compound occurringduring the first portion of the reduction reaction. In general, thissecond metallic sulfide component may be utilized in any amount which iscatalytically effective; ordinarily, satisfactory results are obtainedwith a catalyst containing, on an elemental basis, about 0.1 to about 15wt. percent of the group VIII metal. For example, excellent results areobtained when the catalyst contains about 1 to about wt. percent of aniron group metal in the form of the metallic sulfide.

This group VIII transition metal component may be incorporated in thecatalyst in any suitable manner and in any stage of the preparation ofthis catalyst. One method involves impregnation of the porous carriermaterial with a suitable solution of a group VIII transition metal,another method involves cogellation or coprecipitation of the group VIIIcomponent with a carrier material when it is a refractory inorganicoxide. The preferred method involves impregnation of the carriermaterial with an aqueous solution containing a water-soluble,decomposable group VIII metalcontaining compound such as iron acetate,iron bromide, iron chloride, iron nitrate, iron oxalate, iron sulfate,cobalt acetate, cobalt bromide, cobalt chloride, cobalt nitrate, cobaltsulfate, nickel bromide, nickel perchlorate, nickel chloride, nickelformate, nickel nitrate, nickel sulfate, ammonium chloroplatinate,chloroplatinic acid, bromoplatinic acid, platinum dichloride, palladiumchloride, palladium sulfate,-palladium nitrate and the like compounds.Like the previous metallic sulfide component, this component may beadded before, during or after the addition of the other metallic sulfidecomponent, with best results ordinarily obtained by sequentialimpregnation with an intervening sulfide treatment. For example, in themore preferred case where the group VIII metallic sulfide component iscobalt sulfide, excellent results are obtained with a two-stepimpregnation procedure separated by an intervening sulfide treatment aswas previously disclosed in connection with the first metallic sulfidecomponent.

Regarding the relative amounts of the metallic components of the presentcatalyst, I have found it to be a good practice to specify the amount ofthe group VII component as a function of the amount of the group VIBcomponent. On this basis, the amounts of the group VIII and the groupVIB components should ordinarily be selected from the ranges previouslygiven so that the atomic ratio of group VIII metal to group VIB metalcontained in the catalyst is about 0.25:1 to about 5:1. For example, inthe case of the preferred cobalt sulfideand molybdenumsulfide-containing catalyst, the amounts of cobalt and molybdenum arepreferably selected so that the atomic ratio of cobalt to molybdenum isabout 0.25 l to about 5:1.

Regardless of the details of how the metallic sulfide components arecombined with the porous carrier material the final catalyst generallywill be dried at a temperature of about 200 to 600 F. for a period of 2to about 24 hours or more. In the case where the porous carrier materialis a refractory inorganic oxide, the resulting dried composite can befurther oxidized or calcined in an air atmosphere at a temperature ofabout 700 to about l,l00 F. for an additional period of about 0.5 toabout 10 hours. In the case where the porous carrier material is acarbonaceous material, this calcination step is not essential, and ifits performed, it should be done in an inert environment such as in thepresence of nitrogen. In either case, it is a distinctly preferredpractice to subject the resulting catalyst to a sulfiding step prior toits use in the present method, in order to insure that both metalliccomponents are in the sulfide state. Preferably, this presulfidingtreatment Ill takes place in the presence of a suitable decomposablesulfur-containing compound such as lower molecular weight mercaptans,hydrogen sulfide, organic sulfides and the like. Typically, thesulfiding procedure involves contacting the dried catalyst with thesulfur-containing reactant at conditions sufficient to effect thedesired incorporation of sulfur generally including a temperature ofabout 50 to about 1,lO F. It is to be noted that the preferred catalystpreparation procedure involves sequential impregnation of the metallicsulfide component with a sulfide treatment of the resulting catalystafter each impregnation step.

Although the sulfiding treatment may be conducted according to any ofthe procedures known to the art, I have found that the preferredtechnique involves using a H s-containing gas to quench a vacuum aboutthe catalyst. That is, this technique involves establishing a vacuum ina closed vessel containing the catalyst and thereafter injecting HS-containing gas into the vessel to return same at least to atmosphericpressure. The pressure in the vessel during the first portion of thisprocedure should be less than 0.2 atoms and preferably less than 0.05atoms. This technique may be separated, if desired, until the catalystdoesnt absorb any further amounts of H 8.

The principal advantage associated with the use of this bimetalliccatalyst in the method of the present invention is its increasedactivity for accelerating the reaction between hydrogen and theoxysulfur compound. This relatively high activity allows the reductionreaction to be conducted at conditions which are relatively low inseverity, thereby effecting savings in utilities associated with thereduction method such as cost of heat generation, hydrogen compressioncosts and the like costs. In addition, this bimetallic catalystmainfests a rather high selectivity for the corresponding sulfidecompound, thereby limiting the yield of undesired byproducts. Forexample, a catalyst comprising molybdenum sulfide and cobalt sulfidecombined with an activated carbon carrier material in an amountsufficient to result in a composite containing, on an elemental basis,2.3 wt. percent molybdenum and 4.6 wt. percent cobalt at 150 C. achieved100 percent conversion of sodium thiosulfate at a selectivity forsulfide of 97 percent.

According to the method of the present invention, the aqueous solutioncontaining the oxysulfur compound and the hydrogen stream are contactedwith this bimetallic catalyst at reduction conditions. The instantreduction method can be carried out in any suitable manner and in eithera batch or continuous type operation. In a batch system, the aqueoussolution containing the oxysulfur compound is charged to a reaction zonewhich is thereafter charged with the desired amount of hydrogen. Thecatalyst is mixed with the reactants in the reaction zone and agitationand heat is supplied to the zone in order to initiate the desiredreaction. In a continuous type system the oxysulfur-containing aqueousstream is passed into the reaction zone in either upward, radial ordownward flow with a hydrogen stream being simultaneously charged to thereaction zone in either concurrent or countercurrent flow relative tothe aqueous stream. In particular, a preferred embodiment of the instantmethod involves concurrent flow of the aqueous stream and the hydrogenstream into a reaction zone containing the previously characterizedbimetallic catalyst. Although any of the modes of operation known to theart for using a solid catalyst can be utilized in the present inventionincluding a moving bed system or a fluidized bed type system, thepreferred procedure involves maintaining the catalyst within thereaction zone as a fixed bed of relatively small particles. Typically,good results are obtained when the particle size is 10 to 30 mesh (U.S.standard sieve series).

In the preferred concurrent flow embodiment, the effluent streamwithdrawn from the reaction zone primarily contains the sulfide productof the reduction reaction, a minor amount of unreacted oxysulfurcompound, unreacted hydrogen and water. The hydrogen is typicallyseparated from the aqueous effluent stream in a conventional separatingzone, and the resulting hydrogen stream recycled through a suitablecompressing means to the reaction zone. If desired, the sulfide productmay be stripped from the resulting aqueous effluent stream via asuitable stripping agent such as by injecting the sulfide-containingsolution into a stripping column and utilizing steam or any othersuitable stripping gas to remove hydrogen sulfide overhead with recoveryof substantially sulfide-free aqueous solution from the bottom of thestripping column. The hydrogen sulfidecontaining overhead stream maythen be processed by conventional techniques to recover sulfur, toproduce sulfuric acid or to make any other desired sulfur product. Theaqueous solution withdrawn from the bottom of this stripping column thenmay be discharged or disposed of in any suitable manner without causingany substantial waste disposal problem since it has only a relativelysmall biological oxygen demand. In some cases the aqueous effluentstream containing the sulfide compound can be directly used in furtherprocessing or it can be returned to the process which originallyproduced the oxysulfur-containing input stream to the present method.

The reduction conditions utilized in the method of the present inventionare generally characterized as reduction conditions effective to convertoxysulfur compounds to the corresponding sulfide compound. The reactiontemperature is preferably selected from the range of about 50 to about350 C., with a preferred value being about to 200 C. The pressureutilized should be sufficient to maintain at least a portion of theinput aqueous solution in the liquid phase. In general, a pressure abovethis minimum pressure is preferred because I have noted that the extentof conversion increases with increasing pressure. However, the use of anextremely high pressure is relatively costly, accordingly, pressures ofabout to about 3,000 psig. are preferred. In a batch embodiment of thepresent method, the contact time utilized is preferably about one-halfto about 5 hours, with best results obtained at 0.75 to about 2.5 hours.In a continuous process, it is preferred to use a LHSV (defined on thebasis of the charge rate of the input solution divided by the volume ofthe catalyst bed) in the range of about 0.25 to about 10 hrs, with bestresults obtained at about 0.5 to about 3 hrs.

The following examples are given to illustrate further the preferredmode of operation and utility of the present invention. These examplesare intended to be illustrative rather than restrictive.

EXAMPLE I In order to demonstrate the beneficial effect of thepreviously described bimetallic catalyst, three catalysts were prepared.Catalyst A" was a combination of molybdenum sulfide with a Darco carboncarrier material in an amount such that the catalyst contained on anelemental basis, 2.1 wt. percent molybdenum. Catalyst A was prepared byimpregnating a to 30 mesh particle of a Darco carbon carrier materialwith molybdic acid, drying the resulting impregnated carrier andthereafter sulfiding with hydrogen sulfide at room temperature. CatalystB was a combination of cobalt sulfide with a Darco carrier materials inamounts sufficient to result in a catalyst containing 4.6 wt. percentcobalt. Catalyst B was prepared by a procedure similar to that used forCatalyst A except the impregnation solution contained cobalt acetaterather than molybdic acid. Catalyst C, the catalyst of the presentinvention, was a combination of molybdenum sulfide and cobalt sulfidewith Darco carbon in an amount sufficient to result in a catalystcontaining, on an elemental basis, 2.3 wt. percent molybdenum and 4.6wt. percent cobalt. Catalyst C was prepared by impregnating the 10 to 30mesh particles of Darco carrier material with cobalt acetate at roomtemperature, drying the resulting impregnated carrier material andtreating the resulting dried material with hydrogen sulfide at roomtemperature, thereafter impregnating the sulfided carrier material withan aqueous solution of molybdic acid, drying as before and treating withhydrogen sulfide in order to convert the molybdenum to molybdenumsulfide. The atomic ratio of cobalt to molybdenum in catalyst C was3.5:1.

The resulting catalyst were utilized in a series of test to determinetheir relative activity for the reduction of an aqueous solution of anoxysulfur compound with hydrogen. In this test, the input aqueoussolution was an aqueous solution of sodium thiosulfate containing 9.08wt. percent sulfur in the form of thiosulfate. The comparison tests wereall made in a pilot plant wherein each catalyst was loaded into aconventional reaction zone and the mixture of aqueous solution andhydrogen stream was passed downflow into the reaction zone. Theconditions utilized in this test were a pressure of 500 psig., a LHSV ofl hrs." and a mole ratio of hydrogen to sodium thiosulfate of 4: l. Thereaction temperatures utilized in each run are given in the followingTable 1. Each test run consisted of an 8 hour lineout period and an 8hour test period. The results of these comparison runs are presented inTable I in terms of reaction temperature utilized, percent of sodiumthiosulfate charged to the reactor that was converted therein andselectivity for sulfide expressed as percent of converted thiosulfatewhich went to sulfidetypically sodium sulfide or sodium hydrosulfide.

With reference now to Table I, it can be seen that Catalyst A producedvery poor results with a reaction temperature of 170 C. Since reactiontemperatures required to achieve a given conversion is a sensitiveindicator of catalyst activity, it is apparent that Catalyst "A" wasrelatively inactive for the desired reduction reaction. Likewise,Catalyst 8" was relatively inactive although it did much better thanCatalyst A. Specifically, Catalyst B achieved a 58 percent conversion at150 C. and a 26 percent conversion at 129 C. 1n sharp contrast, CatalystC, the catalyst of the present invention, possessed high activity forthe desired conversion reaction at both 150 and 128 C. The results forthese last two temperatures are a conversion of percent at C. at aselectivity for sulfide of 99 percent, and a conversion of 70 percent ofthiosulfate at 128 C. at a selectivity for sulfide of 98 percent.

These results manifest the surprising increase in activity for thedesired reduction reaction which is achieved by means of the preferredbimetallic catalyst of the present invention.

EXAMPLE II The catalyst utilized is a combination of tungsten sulfideand iron sulfide with a carbonaceous carrier material in amountssufficient to result in a composite containing on an elemental basis, 5wt. percent iron and 3 wt. percent tungsten. The input aqueous stream isa solution of sodium bisulfite containing 5 wt. percent su1 fur asNaI-ISO The reaction conditions utilized in an experiment similar tothat described in Example 1 are: an inlet reactor temperature of- C., apressure of 750 psig., a LHSV of 1 hrsf, and a hydrogen to sulfide moleratio of 10:1. Results of a ten hour test period indicate that a majorportion of the sodium sulfite is converted to sodium hydrosulfide.

EXAMPLE Ill The catalyst is a combination of chromium sulfide and nickelsulfide with a gamma-alumina carrier material in amounts sufficient toresult in a composite containing, on an elemental basis, 2 wt. percentchromium and 5 wt. percent nickel. The input aqueous solution containsabout 5 wt. percent sulfur in the form of ammonium trithionate i. e.(NI-10 8 0 The conditions utilized in an experiment similar to thatdescribed in Example I are: an inlet reactor temperature of 200 C., apressure of 500 psig., a LHSV of 1.5 hrs. and a hydrogen to trithionatemole ratio of 6:1. Results indicate good conversion of the ammoniumtrithionate at a relatively high selectivity for ammonium hydrosulfide.

It is intended to cover by the following claims all changes andmodifications of the above disclosure of the present invention thatwould be self-evident to a man of ordinary skill in the catalyticwater-treating art.

I- claim as my invention:

1. A method for reducing an inorganic, water-soluble oxysulfur compoundto a sulfide compound, which comprises contacting an aqueous solution ofsaid oxysulfur compound and hydrogen with a catalyst, comprising acombination of catalytically effective amounts of a group VIB metallicsulfide component and of a group VlIl metallic sulfide component with aporous carrier material, at a temperature of from about 50 to about 350C. and a pressure of about 100 to about 3,000 psig.

2. A method as defined in claim 1 wherein said oxysulfur compound is awater-soluble, inorganic sulfite compound.

3. A method as defined in claim 2 wherein said sulfite compound isselected from the group consisting of the sulfites and bisulfites ofammonia, the alkali metal and the alkaline earth metals.

4..A method for reducing an inorganic water soluble thiosulfate compoundto a sulfide compound, which comprises contacting an aqueous solution ofsaid thiosulfate compound and hydrogen with a catalyst, comprising acombination of catalytically effective amounts of a Group VIB metallicsulfide component and of a Group VIII metallic sulfide component, with acarbonaceous carrier material, at a temperature of from about 50 toabout 350 C. and a pressure of about 100 to about 3,000 psig.

5. A method as defined in claim 4 wherein said thiosulfate compound isselected from the group consisting of ammonium thiosulfate, the alkalimetal thiosulfates and the alkaline earth metal thiosulfates.

6. A method as defined in claim 5 wherein said thio sulfate compound issodium thiosulfate.

7. A method as defined in claim 5 wherein said thiosulfate compound isammonium thiosulfate.

8. A method as defined in claim 1 wherein said oxysulfur compound is awater-soluble, inorganic polythionic compound.

9. A method as defined in claim 1 wherein said group VIB metallicsulfide component of said catalyst is molybdenum sulfide.

10. A method as defined in claim I wherein said group VIII metallicsulfide component of said catalyst is cobalt sulfide.

11. A method as defined in claim 1 wherein said porous carrier materialis a carbonaceous material.

12. A method as defined in claim 11 wherein said carbonaceous materialis activated carbon.

13. A method as defined in claim 1 wherein said porous carrier materialis a refractory inorganic oxide.

14. A method as defined in claim 13 wherein said refractory inorganicoxide is alumina.

15. A method as defined in claim 4 wherein the Group VIB metallicsulfide component is molybdenum sulfide, and the Group VIII metallicsulfide component is cobalt sulfide.

16. A method as defined in claim 15 wherein said thiosulfate compound isammonium thiosulfate.

17. A method as defined in claim 15 wherein said thiosulfate compound issodium thiosulfate.

18. A method as defined in claim 15 wherein the porous carrier materialis activated carbon.

19. A method as defined in claim 15 wherein hydrogen is present in anamount corresponding to a mole ratio of hydrogen to said thiosulfatecompound of about 6:1 to about 40:1.

20. A method as defined in claim 15 wherein said molybdenum sulfidecomponent of the catalyst comprises about 0.01 to about 10 wt. percentthereof, calculated on an elemental molybdenum basis.

21. A method as defined in claim 15 wherein the cobalt sulfide componentof the catalyst comprises about 0.1 to about 15 wt. percent thereof,calculated on an elemental cobalt basis.

22. A method as defined in claim 15 wherein the amounts of the cobaltsulfide component and the mo lybdenum sulfide component contained in thecatalyst are selected to result in an atomic ratio of cobalt tomolybdenum of about 0.25:1 to about 5:1.

23. A method as definedin claim 15 wherein said reduction conditionsinclude a temperature of about 50 to about 350 C. and a pressure atleast sufficient to maintain a portion of the aqueous solution in theliquid phase.

2. A method as defined in claim 1 wherein said oxysulfur compound is awater-soluble, inorganic sulfite compound.
 3. A method as Defined inclaim 2 wherein said sulfite compound is selected from the groupconsisting of the sulfites and bisulfites of ammonia, the alkali metaland the alkaline earth metals.
 4. A method for reducing an inorganicwater soluble thiosulfate compound to a sulfide compound, whichcomprises contacting an aqueous solution of said thiosulfate compoundand hydrogen with a catalyst, comprising a combination of catalyticallyeffective amounts of a Group VIB metallic sulfide component and of aGroup VIII metallic sulfide component, with a carbonaceous carriermaterial, at a temperature of from about 50* to about 350* C. and apressure of about 100 to about 3,000 psig.
 5. A method as defined inclaim 4 wherein said thiosulfate compound is selected from the groupconsisting of ammonium thiosulfate, the alkali metal thiosulfates andthe alkaline earth metal thiosulfates.
 6. A method as defined in claim 5wherein said thiosulfate compound is sodium thiosulfate.
 7. A method asdefined in claim 5 wherein said thiosulfate compound is ammoniumthiosulfate.
 8. A method as defined in claim 1 wherein said oxysulfurcompound is a water-soluble, inorganic polythionic compound.
 9. A methodas defined in claim 1 wherein said group VIB metallic sulfide componentof said catalyst is molybdenum sulfide.
 10. A method as defined in claim1 wherein said group VIII metallic sulfide component of said catalyst iscobalt sulfide.
 11. A method as defined in claim 1 wherein said porouscarrier material is a carbonaceous material.
 12. A method as defined inclaim 11 wherein said carbonaceous material is activated carbon.
 13. Amethod as defined in claim 1 wherein said porous carrier material is arefractory inorganic oxide.
 14. A method as defined in claim 13 whereinsaid refractory inorganic oxide is alumina.
 15. A method as defined inclaim 4 wherein the Group VIB metallic sulfide component is molybdenumsulfide, and the Group VIII metallic sulfide component is cobaltsulfide.
 16. A method as defined in claim 15 wherein said thiosulfatecompound is ammonium thiosulfate.
 17. A method as defined in claim 15wherein said thiosulfate compound is sodium thiosulfate.
 18. A method asdefined in claim 15 wherein the porous carrier material is activatedcarbon.
 19. A method as defined in claim 15 wherein hydrogen is presentin an amount corresponding to a mole ratio of hydrogen to saidthiosulfate compound of about 6:1 to about 40:1.
 20. A method as definedin claim 15 wherein said molybdenum sulfide component of the catalystcomprises about 0.01 to about 10 wt. percent thereof, calculated on anelemental molybdenum basis.
 21. A method as defined in claim 15 whereinthe cobalt sulfide component of the catalyst comprises about 0.1 toabout 15 wt. percent thereof, calculated on an elemental cobalt basis.22. A method as defined in claim 15 wherein the amounts of the cobaltsulfide component and the molybdenum sulfide component contained in thecatalyst are selected to result in an atomic ratio of cobalt tomolybdenum of about 0.25:1 to about 5:1.
 23. A method as defined inclaim 15 wherein said reduction conditions include a temperature ofabout 50* to about 350* C. and a pressure at least sufficient tomaintain a portion of the aqueous solution in the liquid phase.